This invention relates to the recovery of metals from low level sources by extraction. More particularly, it is concerned with an improved resin sorption process for recovering tungsten from low level sources containing relatively high levels of contaminating boron.
Tungsten is an important component of alloy-hardened metals and is indispensable in the manufacture of electric heating elements and lamp filaments. The increasing value and scarcity of this vital metal require that efficient methods be found for recovering tungsten from low level sources. Important low level sources of tungsten are natural alkaline brines such as those of Searles Lake, Calif. Searles Lake is estimated to contain approximately 170 million pounds of tungsten trioxide, but at concentrations of only 50-70 parts per million.
Various processes have been proposed for the recovery of tungsten from such brines, but most are complex and result in the consumption of large amounts of reagent chemicals per pound of tungsten recovered or present problems of pollution or process waste disposal. U.S. Pat. No. 4,180,628 discloses a method of recovering tungsten from natural brines by employing a resin to sorb the metal values from solution followed by desorption of the metals from the resin using water or an alkali metal carbonate solution to recover the tungsten.
The tungsten recovered by prior art processes, however, often contains unacceptable levels of contaminating boron which must be removed by further processing steps before the tungsten can be advantageously used. The problem of boron contamination is particularly acute when the source of tungsten is a natural brine which contains low levels of the metal together with comparatively large amounts of borate salts.